Whenever multiple transverse mode (multimode) lasers, such as broad-area laser diodes or phase-locked diode laser arrays, are operated in a pulsed manner with high peak power outputs, pulse jitter may occur. Pulse jitter is a change or variation in the observed optical power output, either between different pulses in a series of pulses or within a single pulse. If all of the optical power emitted from the laser is collected, there is usually very little pulse jitter. However, if the optical beam is apertured, i.e. passes through some kind of aperture whereby only a portion of the total optical power output is collected, then pulse jitter is greatly enhanced. The aperture may be a physical aperture, such as a stop or a lens system, an optical fiber, or a virtual aperture which behaves like a physical aperture.
Pulse jitter is caused by the laser switching between several or many of the available transverse modes of operation. Mechanisms causing switching may include thermal effects or optical feedback into the laser cavity. Because the available power is shared by the operating modes in a laser, very little variation in total output power is observed in an unapertured beam. However, due to the different angular directions of light output from the various laser modes, as such modes switch on and off, an apertured beam will vary in intensity, hence the enhanced pulse jitter.
An object of the present invention is to provide a method of reducing pulse jitter in laser diodes and diode laser arrays, leading to a more stable power output per pulse, even when the optical beam is apertured.